Relief device for offset stacker tamping mechanism

Abstract: A relief device for the tamping mechanism (176) of an offset sheet set stacker. A sheet set stacker is provided having a plurality of retractable tamping mechanisms for alternately offsetting sheet sets within the stacker. Each tamping mechanism (176) is provided with a spring biased follower arm (206) which locks the tamping mechanism (176) in an operative position. A relief device in the form of an oblong pivot mount allows the tamping mechanism (176) to not only pivotally retract from an operative position but to also shift a slight amount transversely to the paper path process direction. This slight shift prevents a binding of the tamper against the just compiled sheet stack (214) and minimizes the occurrence of sheet stack disturbance.

Description: This invention relates generally to an apparatus for offset stacking of sheet sets. US-A-5,188,353 which represents the closest prior art discloses a disk stacker having a tampering mechanism located over a sheet-receiving platform according to the features in the preamble of claim 1. First and second registration walls are provided, each wall having a tamper located adjacent to the wall and movable through an aperture therein. The tamper has an active position and inactive position and the tamper on each side registration wall operate alternately to offset stacks from one side to the other as each sheet set is discharged to the stacker. The present invention has as a main object the provision of means for preventing the jamming of the tamping mechanism of the stacking apparatus and disturbance of the stacked sheet sets. Accordingly, the present invention provides an apparatus in accoordance with appended claims 1 to 8. Also provided is an electrophotographic printing machine in accordance with appended claim 9. In accordance with one embodiment of the present invention, there is provided an apparatus for preventing sheet stack disturbance in a sheet stacker. The apparatus comprises a first registration member defining an aperture therein and a second registration member opposed from the first the registration member. There is also provided a first tamping mechanism located adjacent the first registration member, adapted to be movable through the aperture defined in the first registration member, the first tamping mechanism being movable between an inactive position located within the first registration member and an active position extending beyond the first registration member, the first tamping mechanism being adapted to oscillate, in the active position to tamp incoming sheets against the second registration member. There is also provided in a characterizing aspect a first means for relieving a force exerted on the first tamping mechanism by a sheet stack formed within the sheet stacker. Pursuant to another embodiment of the present invention, there is provided an electrophotographic printing machine of the type having a stacking device in which sets of sheets are stacked alternately offset from one another in a cross process direction, the stacking device having an apparatus to prevent sheet stack disturbance. The present invention will be described further, by way of example, with reference to the accompanying drawings, in which:- Figure 1 is a schematic perspective view of a stacking tray incorporating first and second tampers which can be used as the cross direction offsetting mechanism incorporating the present invention, wherein one of the tampers is illustrated in an active position and the other tamper is shown in an inactive position behind its side registration wall; Figures 2A, 2B and 2C illustrate a prior art tamping mechanism in the retracted, partially extended, and fully extended tamping positions, respectively; Figures 3A, 3B and 3C illustrate a tamping mechanism utilizing the jam-prevention device of the present invention in the retracted, extended, and relief positions, respectively; and Figure 4 is a perspective view of a printing machine and document outputting device which incorporates two disk stackers according to the present invention and also illustrates a stack of copy output compiled by one of the stackers in which individual sets of copies are offset from one another in the cross-process direction. For a general understanding of the features of the present invention, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to identify identical elements. Figure 4 depicts a typical document output device 10 incorporating two disk stackers 20. It will become evident from the following discussion that the relief mechanism of the present invention may be employed in a wide variety of devices and it's not specifically limited in its application to the particular embodiment depicted herein. Turning to Figure 1, illustrating a stacking tray, the area of the stacker which receives inverted sheets from rotatable disks, includes a pair of side registration walls 183, 184 against which side edges of the sheets 214 are registered; in addition to elevator platforms 170; a registration wall 132 which contacts the lead edge of a sheet; and a trail-edge guide (not shown) which contacts the trail-edge of a sheet. Side registration walls 183, 184 can be fixed relatively to front registration wall or laterally movable, so that sheets having a variety of widths can be located between side registration walls 183, 184. The tamping mechanism 176, 178 is provided to tamp sheets against one of the side registration walls so that the side edges of all the sheets of a set are appropriately aligned. The present invention provides a tamping mechanism which is capable of tamping the side edges of different sheets against one or the other of the side registration walls so that the sets of sheets can be offset from one another in a direction transverse to the process direction. The tamping mechanism includes first and second tampers respectively, each of which includes a tamping finger respectively. Each side registration wall can have more than one tamper. Each tamper moves through an aperture located in the first and second registration walls respectively, between an active position wherein the tamper is extended through its respective registration wall aperture and located above a surface of the sheet stack to tamp incoming sheets against the opposite side registration wall, and an inactive position wherein the tamper is retracted behind its respective registration wall out of the area between the first and second registration walls. Turning next to figures 2A through 2C, the tamping mechanism 276 of the prior art is illustrated. As seen in figure 2A, initially the tamper is in retracted position behind the registration wall 183. Upon rotation of an input crank 142, the tamper finger 140 is rotated as a result of the connecting linkage through an aperture 175 (Fig. 1) in the registration wall 183 to a position adjacent the sheet stack 214. A wire bail 186 arrangement is rotated down upon the top of the tray bottom surface or previously stacked sheet sets 214 to provide a registration guide. The input crank 142 rotation is then stopped by use of a clutch (not shown), and the tamping arm 140 is oscillated back and forth in a horizontal direction so that each incoming sheet is registered against the opposing registration wall. A locking mechanism 145 including a link and cam is connected in common with crank 142 to prevent the tamping mechanism 148 from shifting while in the operative position. Once the set of sheets is fully registered, the tamper mechanism 276 must then be retracted back into the registration wall 183. In the illustrated embodiment of the prior art, as a result of the connecting linkages 145, 146, 147 and the necessity for all of the pivot points to be fixed, the wire bail 186 is often wedged against the sheet stack 214. The force exerted against the wire bail 186 by the sheet stack 214 often inhibits the retraction of the tamping mechanism 148 back into the registration wall or causes a jerking motion which disturbs the just registered and offset stack of sheets. The detailed operation of this mechanism is described in US-A-5,188,353 commonly assigned to the assignee herein, the relevant portions of which are herein incorporated by reference. Referring now to figures 3A through 3C, the tamping mechanism 176 including the relief mechanism of the present invention is illustrated. Figure 3A illustrates the tamping mechanism 176 in the retracted position. Referring next to 3B it can be seen as the input crank 200 is rotated the tamping arm assembly 208 is caused to be extended through the registration wall 183 and into an active position by means of the connecting link 202. A spring 204 biases a follower arm 206 riding against the tamping arm assembly 208 and causes the tamping finger 210 to be locked in an active position when a lug on the tamping arm assembly 208 meshes with a detent in the follower 206. This assures that all of the sheets of the set being tamped are registered fully against the opposing registration wall. Once each set is fully compiled and registered, the input crank 200 is again rotated and the tamping mechanism 208 is retracted into the registration wall 183. Should the wire bail 211 be wedged against the sheet stack 214 as previously described, the illustrative mechanism provides for a slight movement away from the sheet stack, as seen in Fig. 3C, by the wire bail 211 and tamping arm assembly 208 prior to retracting the arm. This slight movement is provided as a result of the elongated pivot mount 212 in the tamping arm assembly 208 and the spring biased follower assembly 206. The force of the stack 214 causes the tamping arm assembly 208 to be moved away from the stack 214 against the spring force of the follower 206. As the follower 206 is independently movable in a direction away from the stack 214 the tamping arm assembly 208 is not hindered as it is retracted into the inactive position. This slight movement in the cross-process direction relieves the pressure against the wire bail 211 and allows for retraction of the tamping mechanism 208 into the registration wall 183 without disturbance of the compiled sheet set 214 in the stacker. In recapitulation, there is provided a relief device for a sheet stacker which prevents the disruption of the stacked and offset sets of sheets in the stacking apparatus. The relief device includes a spring-biased follower mechanism on the individual set tamping mechanism, used to lock the tamper in the operative position, and an elongated pivot point which allows the tamping mechanism to pull away slightly from a just compiled set of sheets prior to retracting. This improvement allows the tamping mechanism to accurately align and offset alternate sets of sheets and to retract within the registration wall without upsetting the just registered sheet stack.

Claims: An apparatus for preventing sheet stack disturbance in a sheet stacker, comprising: a first registration member (183) defining an aperture (175) therein; a second registration member (184) opposed from said first said registration member (183); a first tamping mechanism (176) located adjacent said first registration member (183) adapted to be movable through the aperture (175) defined in said first registration member (183), said first tamping mechanism (176) being movable between an inactive position located within said first registration member (183) and an active position extending beyond said first registration member (183), said first tamping mechanism (176) being adapted to oscillate, in the active position, to tamp incoming sheets against the second registration member (184); characterised by first relieving means for relieving a force exerted on said first tamping mechanism (176) by a sheet stack (214) formed within the sheet stacker. An apparatus according to Claim 1, characterised by actuating means for moving said first tamping mechanism (176) between the inactive and active positions. An apparatus according to Claim 1 or Claim 2, characterised by a second tamping mechanism (178) located adjacent said second registration member (184), said second registration member (184) defining an aperture therein, said second tamping mechanism (178) being movable between an inactive position located within said second registration member (184) and an active position extending beyond said second registration member (184), said second tamping mechanism (178) being adapted to oscillate, in the active position, to tamp incoming sheets against the first registration member (183); and further characterised by second relieving means for relieving a force exerted on said second tamping mechanism (178) by a sheet stack (214) formed within the stacker. An apparatus according to Claim 3, characterised by further actuating means for moving said second tamping mechanism (178) between the inactive and active positions. An apparatus according to Claim 2 or Claim 4, characterised by locking means for locking said first and/or said second tamping mechanisms in the active position. An apparatus according to Claim 5, characterised in that the or each tamping mechanism has its associated locking means including a follower member (206) adapted to contact said tamping mechanism (176), said follower member (206) defining a detent therein and said tamping mechanism (176) having a lug thereon, said lug meshing with the detent in response to said tamping mechanism (176) being in the active tamping position; and urging means (204) for biasing said follower member (206) against said first tamping mechanism (176). An apparatus according to any one of claims 1 to 6, characterised in that said first relieving means comprises: a first tamping finger (210); and a first tamping base member pivotally connected at a first end to said first tamping finger (210) and pivotally connected at a second end to said first registration member (183) so as to be retractable through the aperture (175) therein, said base member defining an elongated pivot mount so as to be moveable in a direction transverse to the process direction as well as pivotally. An apparatus according to Claim 3 or 4, characterised in that said second relieving means comprises: a second tamping member; and a second tamping base member pivotally connected at a first end to said second tamping member and pivotally connected at a second end to said second registration member so as to be retractable through the aperture therein from an active to an inactive position, said base member defining an elongated pivot mount at the second end so as to be moveable in a direction transverse to the process direction as well as pivotally. An electrophotographic printing machine of the type having a stacking device in which sets of sheets are stacked alternately offset from one another in a cross-process direction, characterised in that the stacking device has an apparatus to prevent sheet stack disturbance, the apparatus being in accordance with any one of Claims 1 to 8.

Inventors: LEWIS CARL B, ULRICH VERNON W, LEWIS, CARL B., ULRICH, VERNON W.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1994
Main classification: B65H33
IPC codes: B65H33